The disclosures herein relate generally to computer systems and more particularly to an apparatus and method for electronically encoding an article with work-in-progress information.
The ability to track progression of the assembly and testing of an article relies upon the ability to track certain work-in-progress information. A printed circuit assembly illustrates one example of an article for which it is highly advantageous to track the work-in-progress information of various assembly operations and tests. Through the tracking of work-in-progress information, estimates of reliability and improvements in manufacturability of the printed circuit assembly, or other article, can be achieved.
Tracking the test progression of an electronic assembly, such as the printed circuit assembly, relies upon the electronic manufacturer having work-in-progress tracking capabilities. Those work-in-progress tracking capabilities vary from supplier site to supplier site and do not offer direct feedback to the customer. There is no technique commonly employed among electronic manufacturers for encoding work-in-progress information such that it can be manually checked as the assembly travels through the assembly and testing operations. Additionally, it is not currently possible to encode historical work-in-progress information on and retrieve it from a particular assembly once it has reached the customer""s site.
Present techniques for tracking work-in-progress information of articles, including printed circuit assemblies, have several limitations. One limitation is that many of the present techniques are costly to implement. Consequently, the quantity of information captured is reduced to lower the cost. Another limitation is that many of the present techniques can retain only a limited amount of work-in-progress information. Such limitations adversely affect the ability to use work-in-progress information to estimate reliability and improve manufacturability.
Test progression of an electronic article has typically been tracked only by a major assembly process step. For example, an assembly process for printed circuit assemblies typically includes operations such as post wave solder touchup, automated visual inspection, low-level manufacturing defect analyzer, high-level in-circuit test, stress process (temperature cycling or vibration), at-speed functional test, and out of box audit (sampling testing).
Typically, a work-in-progress tracking system reads barcodes that are physically located on the assembly. The physical factory location of the assembly is recorded in a database. Sometimes, an assembly will fail one of the process steps for whatever reason and will need to be repaired and tests will need to be repeated. This presents a challenge to work-in-progress tracking software to ensure that the repeated tests actually occur. There is typically not an automated means of verifying that all of the test steps have occurred in the correct order, especially when a re-work operation has occurred.
U.S. Pat. No. 5,043,657 discloses a technique for xe2x80x9cmarkingxe2x80x9d integrated-circuit chips. When large lots of the chips are drift-tested at different temperatures, each chip can be individually identified and associated with the test data accumulated for the particular chip. Fabricating such a chip includes forming additional resistors on each chip with the resistors connected in series to a voltage supply. The resistors are trimmed at the wafer stage to produce voltages, at nodal points between the resistors, having magnitudes that uniquely identify each particular chip. In this manner, each such chip on a printed circuit assembly can be uniquely identified.
U.S. Pat. No. 5,003,251 discloses a barcode that is applied to a printed circuit assembly. The bar code is used for uniquely identifying the printed circuit assembly. When the printed circuit assembly undergoes testing and evaluation, the results are stored in computer memory along with an identification number. Subsequent to the time of testing, the original test data can be reviewed by scanning the barcode such that the results stored in the computer memory are accessed. The barcode may be permanently programmed into an LCD that is mounted on the printed circuit assembly, or may be permanently affixed to the printed circuit assembly on a label. Such a bar-coding system requires additional operations to be carried-out to facilitate correlating data to a particular barcode and for retrieving data associated with a particular barcode.
U.S. Pat. No. 4,437,229 discloses a hybrid integrated circuit package including a circuit assembly on which are formed thin film components of a circuit and to which is bonded at least one semiconductor chip. Prior to bonding the chip to the article, the circuit undergoes various tests and adjustment operations. An electric element, preferably a resistance element, is formed on the article. The element is functionally independent of the circuit. A first, initial value of the element marks the article as belonging to a first group of articles having first circuit characteristics. The initial value of the element is selectively altered to a second value upon a determination that the article has circuit characteristics other than those of the first group. In the described preferred embodiment the first group is a group of electrically acceptable articles, while other characteristics are those of defective articles. The mark is typically altered by a current of sufficient magnitude to burn portions of the element, or by selective application of radiant energy such as a laser beam. Identifying the altered mark permits articles having defective circuits thereon to be selectively eliminated from further processing. The elements are irreversibly altered such that previously used values cannot be reused.
U.S. Pat. No. 4,975,876 discloses a method for arranging a read memory for reading electrically updating status information from an integrated circuit that includes various circuit layers. A plurality of patterned circuit layers, commonly referred to as pattern layers, are produced from respective masks. Each pattern layer has provided therein a separate memory device, such that when changes are made in one such pattern, the updating status of the pattern layer can be written into the memory device in code form. The memory devices in the integrated circuit provide a read-only memory. The read-only memory is programmed so that each pattern layer having a memory device includes a code that is individual to its own updating status. The updating status code is written into the memory device at the same time that the code is written into a test device as reference information. When checking the integrated circuit, a test program in the test device reads the updating status of each pattern layer. The updating status is then compared with the reference information for determining the specific updating status of the integrated circuit. Accordingly, update status of the integrated circuit is coded, but work-in-progress information of an associated assembly is not.
The ability to effectively track present and historical work-in-progress information of an article is essential to estimating the reliability and improving the manufacturability of the article. Tracking only present work-in-progress information of the article limits the degree to which estimates of reliability and improvements in manufacturability can be attained. To make accurate estimation of the reliability of an article and to make significant improvements in the manufacturability of the article, it is necessary to retain present and historical work-in-progress information, regardless of the testing, re-work and repair operations conducted on the article during its manufacture and field use.
Therefore, what is needed is an apparatus and method for enabling an article to be electronically encoded with present and historical work-in-progress information that is associated with the assembly, testing, re-work and repair of the article.
Accordingly, in one embodiment, present and historical work-in-progress information is electronically encoded on a status-encoding device attached to an article. To this end, a method is provided for electronically encoding an article with work-in-progress information. The method includes determining a work-in-progress condition of the article and setting an encoding device attached to the article to a set-point corresponding to the work-in-progress condition.
A principal advantage of this embodiment is that present and historical work-in-progress information of the article are used to effectively estimate the reliability and improve the manufacturability of the article.